Lockheed L-1000 (XJ37)

[KJ_Lesnick]

I was reading about the engine and this is kind of puzzling. 

This is a quote from "Experimental & Prototype U.S. Air Force Jet Fighters" by Dennis R. Jenkins & Tony R. Landis

.....On 30 March 1942, Lockheed submitted preliminary model specifi-
cations for the L-133 jet-powered fighter to the Army.  Given the pres-
sure of producing combat aircraft, the Army expressed little interest in
the L-133 itself, but the L-1000 axial-flow turbojet engines were intrigu-
ing.  The primary features that interested the Army were the axial-flow
compressor and the multi-stage turbine.  At a meeting on 21 August 1942,
researchers from Wright Field commented that the L-1000 appeared
overly complicated, although Lockheed engineers believed them to be
relatively simple.  At this point the engine was 24 inches in diameter, 139
inches long, and weighed 1,235 pounds.  It was expected that the engine
would develop 6,700-pounds-force (lbf) of thrust at takeoff and 2,200 lbf
at 50,000 feet.  Further investigation by Wright Field engineers revealed
several flaws in the L-1000, but the Army felt the engine offered suffi-
cient promise to warrant further development.

Okay, at this stage the engine had an axial flow compressor and turbine, as well as a reciprocating compressor aft of the axial-flow section.  Sure this is a rather bizarre set-up and one that seems overly complicated by our standards.  Regardless, I'm wondering why the design was perceived to be simple by Lockheed and yet over-complicated by the guys at Wright Patterson?

[KJ_Lesnick]

Nobody got anything?

[pyro-manic]

Pure conjecture: The Lockheed engineers thought it straightforward as they designed it, and thus knew it's workings. Whereas the Wright Field peeps had just been shown it for the first time, so there was a degree of "WTF" upon seeing it.

[KJ_Lesnick]

Pure conjecture: The Lockheed engineers thought it straightforward as they designed it, and thus knew it's workings. Whereas the Wright Field peeps had just been shown it for the first time, so there was a degree of "WTF" upon seeing it.

Plausible, but why weren't they able to explain the problems away to Wright Patterson?

[pyro-manic]

It doesn't say that that didn't happen later on.

[wuzak]

I wonder if timing had anything to do with the change.

The L-1000 would have been shown to the AAC at about the same time as, or maybe slightly later than, the Tizard Mission.

The Tizard Mission discussed the Whittle jet, to what detail is unclear.

Given the simplicity of the Whittle design the Lockheed design would have certainly appeared overly complicated. And probably a lot heavier too.

[wuzak]

I have often wondered about the Metrovicks project. It started in 1937, I believe, with the design of the F1 after the principles set out in A A Griffiths' 1926 paper about the design of gas turbines, plus other research Griffiths had undertaken. This was to be an axial flow unit with multi stage compressor, with a single turbine to drive the compressor and a power turbine - the F1 was to be a turboprop. After Whittle demonstrated his jet work on the F1 was stopped and transferred to the F2 - a pure jet.

The F2 (and F1) was far more powerful than the Whittle engine, but also far more complicated. It also suffered from manytechnical difficulties, but eventually evolved into teh Armstrong-Siddeley Sapphire.

The F1 could have been a useful engine for mid war bombers/bomber projects - if the problems could have been sorted out early enough. Turboprops would ahve been more suitable to teh types of speeds that the heavies had then, plus they had much better fuel economy than jets, and also more acceleration for take-off.

[KJ_Lesnick]

I wonder if timing had anything to do with the change.

The L-1000 would have been shown to the AAC at about the same time as, or maybe slightly later than, the Tizard Mission.

That actually is a possibility, though I'm not 100%.  It is interesting nonethelesss

The Tizard Mission discussed the Whittle jet, to what detail is unclear.

Given the simplicity of the Whittle design the Lockheed design would have certainly appeared overly complicated. And probably a lot heavier too.

Firstly: If the design was perceived to be too complicated, why did they keep making it even more complicated rather than less complicated?
1938-1942: Engine evolved as a multi-staged axial flow LP compressor and turbine, with a reciprocating compressor.  Unsure if an afterburner had been added at this stage
1942-1943: Engine evolved as a mixed-flow-compressor with the reciprocating compressors replaced with a three-stage centrifugal-flow compressor with inter-cooling located between each stage, the twin-spooled set-up would be driven by a five-stage axial-turbine, and a hydraulic clutch was used to allow the RPM of the compressor to be varied with altitude (similar to a supercharger, except rather than working faster at high altitude, and slower at low altitude; it worked the opposite).  The design now featured an afterburner.
1943-1946: Engine evolved into a twin-spool axial-flow compressor driven by twin-stage turbines; each compressor had 16-stages with inter-cooling located between them.  Inter-cooling was reduced, the hydraulic-clutching was only attached to the first four stages of the LP-compressor, but the turbine cooling was actually made considerably more advanced -- the blades were hollowed and could include either air or liquid cooling and the afterburner was allegedly actively cooled.

Secondly: How much did the Whittle jet weigh?  This design according to the listed figures was around 1,235 pounds.  That's not that heavy and when you consider the projected output was 6,700 pounds which yields a spectacular power-to-weight ratio.

I have often wondered about the Metrovicks project. It started in 1937, I believe, with the design of the F1 after the principles set out in A A Griffiths' 1926 paper about the design of gas turbines, plus other research Griffiths had undertaken. This was to be an axial flow unit with multi stage compressor, with a single turbine to drive the compressor and a power turbine - the F1 was to be a turboprop. After Whittle demonstrated his jet work on the F1 was stopped and transferred to the F2 - a pure jet.

The F2 (and F1) was far more powerful than the Whittle engine, but also far more complicated. It also suffered from manytechnical difficulties, but eventually evolved into teh Armstrong-Siddeley Sapphire.

Were these technical difficulties made clear to the Tizzard Mission

[wuzak]

Were these technical difficulties made clear to the Tizzard Mission

I think the F2 was still in the process of design at the time of the Tizard mission, the technical difficulties coming later.

Secondly: How much did the Whittle jet weigh?  This design according to the listed figures was around 1,235 pounds.  That's not that heavy and when you consider the projected output was 6,700 pounds which yields a spectacular power-to-weight ratio.

The Power Jets W.1 is listed as weighing 700lb for 850lb thrust. http://en.wikipedia.org/wiki/Power_Jets_W.1
The W.2 weighed more at 950lb, but gave nearly 2,500lb thrust. http://en.wikipedia.org/wiki/Power_Jets_W.2

The Whittle jets had a double sided centrifugal compressor (not 2 stage) and a single axial flow turbine.

The Rolls Royce Welland weighed in at 850lb for 1700lb thrust. http://en.wikipedia.org/wiki/Rolls-Royce_Welland
The de Havilland Goblin/Halford H.1 weighed 1550lb for 3000lb thrust. http://en.wikipedia.org/wiki/Halford_H.1

The L1000would have been behind all of these.

The Metrovicks F2/4 weighed 1750lb for 3500lb thrust. http://en.wikipedia.org/wiki/Metrovick_F.2_Freda
That was a little later, but probab;y around teh sam edevelopment time as the L1000.

Firstly: If the design was perceived to be too complicated, why did they keep making it even more complicated rather than less complicated?
1938-1942: Engine evolved as a multi-staged axial flow LP compressor and turbine, with a reciprocating compressor.  Unsure if an afterburner had been added at this stage
1942-1943: Engine evolved as a mixed-flow-compressor with the reciprocating compressors replaced with a three-stage centrifugal-flow compressor with inter-cooling located between each stage, the twin-spooled set-up would be driven by a five-stage axial-turbine, and a hydraulic clutch was used to allow the RPM of the compressor to be varied with altitude (similar to a supercharger, except rather than working faster at high altitude, and slower at low altitude; it worked the opposite).  The design now featured an afterburner.
1943-1946: Engine evolved into a twin-spool axial-flow compressor driven by twin-stage turbines; each compressor had 16-stages with inter-cooling located between them.  Inter-cooling was reduced, the hydraulic-clutching was only attached to the first four stages of the LP-compressor, but the turbine cooling was actually made considerably more advanced -- the blades were hollowed and could include either air or liquid cooling and the afterburner was allegedly actively cooled.

You're right, it does sound complicated. But the Army were still somewhat uninterested in the engine. Also sounds like the weight targets were optomistic.

[wuzak]

T/W of 1.9355 to 1.  I didn't know the Goblin and Halford H.1 were the same engine!  Regardless, some variants of the Goblin would reach 5,000 to 6,000 pounds of thrust at least by the 1950's (DH Comet)

Those were the later de Havilland Ghosts.


Specifications (Ghost 50)

General characteristics
Type: Turbojet
Length: 121 in
Diameter: 53 in
Dry weight: 2,218 lb

Components
Compressor: Single stage centrifugal flow
Combustors: 10 chambers
Turbine: Single-stage
Fuel type: Kerosene

Performance
Maximum thrust: 5,000 lbf at 10,250 rpm
Overall pressure ratio: 4.6
Specific fuel consumption: 1.02 lb/hr/lbf
Power-to-weight ratio:

http://en.wikipedia.org/wiki/De_Havilland_Ghost


Specifications (D.H Goblin II)

Data from Smith[5]

General characteristics
Type: Turbojet
Length: 107 in (2,718 mm)
Diameter: 50 in (1,270 mm)
Dry weight: 1,550 lb (703 kg)

Components
Compressor: Single sided, centrifugal flow
Combustors: 16 chambers
Turbine: Single stage
Fuel type: Kerosene

Performance
Maximum thrust: 3,000 lbf (13.3 kN) at 10,200 rpm
Overall pressure ratio: 3.3:1
Turbine inlet temperature: 790 °C
Fuel consumption: 3,720 lb/hr (465 imp.gal/hr) (1,687 kg/hr - 2,114 L/hr)
Specific fuel consumption: 1.3 lbf/lb/hr
Thrust-to-weight ratio: 1.9 lbf/lb

http://en.wikipedia.org/wiki/De_Havilland_Goblin

[wuzak]

I think the F2 was still in the process of design at the time of the Tizard mission, the technical difficulties coming later.

So, no mention of it was made at the Tizard mission?

Possibly mentioned as one of the developments. Probably not in detail.

The Power Jets W.1 is listed as weighing 700lb for 850lb thrust. http://en.wikipedia.org/wiki/Power_Jets_W.1

T/W of 1.2143 to 1.  Not impressive by today's standards but by piston engine standards it would have been excellent.

Not sure that it was excellent compared to piston engines of the era. But it was just a starting point.

The W.2 weighed more at 950lb, but gave nearly 2,500lb thrust. http://en.wikipedia.org/wiki/Power_Jets_W.2

2.6158 to 1.  Now that's a considerable improvement and IIRC that design became the Rolls-Royce Welland

The Wellend was a development of the W.2 (the W.2B). The W.2 itself didn't enter production.

Specifications (Welland)
Data from Jane's[1]

General characteristics Type: Turbojet
Length:
Diameter: 43 in (1,098 mm)
Dry weight: 850 lb (386 kg)

Components Compressor:
Fuel type: Aviation kerosene

Performance Maximum thrust: 1,700 lbf (7.7 kN)
Power-to-weight ratio:

http://en.wikipedia.org/wiki/Rolls-Royce_Welland

The L1000would have been behind all of these.

The early L-1000 when it had an axial-compressor, reciprocating compressor, and axial-turbine was 1,235 lbf and produced 6,700 lbf.  That's a T/W of 5.4251 to 1 (admittedly I'm not sure if that's afterburning or not).

The mid-stage L-1000 which had an axial-flow LP compressor, a centrifugal flow HP-compressor with intercooling, a five-stage turbine, and hydraulic clutching to the compressor was around 1,700 lbf and listed power of around 5,000 (and I'm wondering if that number is listed low as the first design was listed at 6,700 lbf).  That yields a power to weight of 2.9 to 1. 

The final L-1000/XJ37 design had a twin-spool axial-flow compressor/axial-turbine, intercooling between the compressor shafts, and hydraulic clutching to the first 4 stages and it's projected weight was 1,600 and thrust was 5,000 or so.  That's a power/weight of 3.125 to 1

That exceeds the listed figures of the British designs.

I was referring to the development timeline, not power/weight.

Still think the thrust was overly optomistic, unless it was with afterburning - which means it isn't reprasentative.

The Metrovicks F2/4 weighed 1750lb for 3500lb thrust. http://en.wikipedia.org/wiki/Metrovick_F.2_Freda
That was a little later, but probab;y around teh sam edevelopment time as the L1000.

T/W of 2:1 -- same as the RR Welland

The F.2/4 was developed into the Armstrong Siddeley Sapphire, which could produce about 8,500lbf thrust for 2,600lbf weight.

Yeah, the reciprocating compressor actually sounded the best choice of all of them.  Lockheed stated they felt the problems were fairly simple and unless they were missing something serious, it seemed to be the one that had the greatest chance for success.  Admittedly removing all that reciprocating junk and just going with a single-spool axial would have been the best option.  At the time though Lockheed might have felt that the USAAF wouldn't accept the design unless the engine was sufficiently close in performance to a piston, and if there were flaws in Price's design -- they couldn't find 'em so they had no real desire to remove them.

The reciprocating compressor ought to give a higher pressure ratio than the axial flow compressors of the time, but would be weightier. And would require the intercooler.

Prior to 1941, Hap Arnold simply wanted to build as many fighters and bombers as he could for the upcoming war; after 1941 he became interested in jets because he realized they could be a game changer and he wanted to get in on it.  I don't know what he knew about the L-1000, but there were people like Dr. Vannevar Bush who told him it would be best to simply license build British engines for starters which was done. 

The Whittle jet did offere the simplest design and (potentially) the fewest pitfalls. It basically had 1 moving part - the compressor (2 sided centrifugal) and turbine (single stage) attached to a shaft. It was likely that this would result in a flyable jet sooner.

Why the L-1000 got more and more complicated might have been suggestions by Wright-Patterson, or Price trying to make his design into something acceptable.  Personally, if I was in Lockheed's shoes, I would have just built the L-1000 as it was, put it on a plane I had available, flown it around and then showed the USAAF the results if there weren't any rules against it or issues of secrecy violations.  Some people only see the value in something when they have results that it works.

Lockheed may not have had the time or money to invest in the development without official backing.

[KJ_Lesnick]

Possibly mentioned as one of the developments. Probably not in detail.

Understood

Not sure that it was excellent compared to piston engines of the era. But it was just a starting point.

I, uh, made a miscalculation -- wrong unit.

Specifications (Welland)
Data from Jane's[1]

Well I understand the listed figures, but I'd almost swear that I saw a figure of 2,200 to 2,400 and considering the W.2 produced 2,500...

I was referring to the development timeline, not power/weight.

Oh, sorry.

Still think the thrust was overly optomistic, unless it was with afterburning - which means it isn't reprasentative.

Well, the possibilities are as follows
1: Thrust was optimistically high
2: Weight was optimistically low
3: Both

As for the AB, could you venture a guess as to what you'd get dry if you had 6,700 lbf wet based on early AB?

The reciprocating compressor ought to give a higher pressure ratio than the axial flow compressors of the time, but would be weightier.

1: Do you have any basic idea how much higher a PR it could produce over an axial-flow HP compressor?
2: How much more would it weigh (keep in mind no combustion occurs in the piston)?

And would require the intercooler.

Where would the intercooler be located?  I assume it would be between the LP compressor and reciprocating HP compressor (theoretically you could put it between the reciprocating compressor and combustion chamber)

Lockheed may not have had the time or money to invest in the development without official backing.

That would explain things.  Is it possible they did not think of the idea?

[wuzak]

As for the AB, could you venture a guess as to what you'd get dry if you had 6,700 lbf wet based on early AB?

Sorry, not a clue.

An example, given in Wiki, is one version of the Armstrong Siddeley Sapphire giving 7500lbf without afterburning, and 9200lbf with.

The reciprocating compressor ought to give a higher pressure ratio than the axial flow compressors of the time, but would be weightier.

1: Do you have any basic idea how much higher a PR it could produce over an axial-flow HP compressor?
2: How much more would it weigh (keep in mind no combustion occurs in the piston)?

1: Early multistage axial flow compressors were giving pressure ratios of around 5, or less. Piston engines of the era could give more, a Merlin having a compression ratio of 6:1, A DB 605 around 8.7:1. These were for supercharged aero engines which had to watch for detonation, so potentially a piston compressor could go higher.

2: Depends on to many factors. Layout, stages, etc.

And would require the intercooler.

Where would the intercooler be located?  I assume it would be between the LP compressor and reciprocating HP compressor (theoretically you could put it between the reciprocating compressor and combustion chamber)

Yes, to reduce the power required to compress the charge in the piston compressor it would need to be cooled after the initial compressor stages.

[KJ_Lesnick]

Sorry, not a clue.

It was worth a shot

An example, given in Wiki, is one version of the Armstrong Siddeley Sapphire giving 7500lbf without afterburning, and 9200lbf with.

I've done some comparisons to the J35 and the figures you gave me for the Sapphire and based on those rules of thumb if 6,700 was AB, then 5,070 to 5,462 lbf.

1: Early multistage axial flow compressors were giving pressure ratios of around 5, or less. Piston engines of the era could give more, a Merlin having a compression ratio of 6:1, A DB 605 around 8.7:1. These were for supercharged aero engines which had to watch for detonation, so potentially a piston compressor could go higher.

Turbo's didn't have the same problems with pre-detonation though, correct? 

2: Depends on to many factors. Layout, stages, etc.

Which I don't have any info on since I don't know the engine layout.

Yes, to reduce the power required to compress the charge in the piston compressor it would need to be cooled after the initial compressor stages.

Okay

[wuzak]

Turbo's didn't have the same problems with pre-detonation though, correct?

Correct, as gas turbines have continuous combustion.